I believe that the opinions posted above are brilliant.. well done everyone! I agree with most of you about Snape's history with the Potters. It would only make since for him to have feelings for Lily because not only was she a pretty and popular girl, but she shared many of Snape's talents including that of potions (as Slughorn suggested in the 6th book). He hid his true feelings for her by calling her names like "mudblood" in order to avoid the merciless torment that James and his friends provided. During this time, I believe, as James began to date Lily, Snape's hatred continues to grow. Snape turns to Voldemort as his way to vent his grief. As Snape becomes a Death Eater, at some point, James Potter spares his life. Snape becomes confused and upset that his archrival- whom he has hated his whole life- saved him. Snape now must rethink everything he has previously thought about the potter family. Shortly after, Snape decides to go and talk to Dumbledore about seeking protection from Voldemort and hopefully gain his trust. This takes him to the bar in which Snape hears the prophecy (the WHOLE prophecy) and Snape is again torn. Should he tell his master and earn his high favor or protect Lily and James and their son? He tells Voldemort only half of the prophecy in hopes that he can be in his master's favor while avoiding the outcome that he fears for the Potters. When he finds out what Voldemort wants to do (eliminating the threat), Snape decides once and for all that he must prevent this. He goes to Dumbledore and tells him everything. Dumbledore's "concrete proof" that Snape isn't trying to trick him?
His love for Lily Potter. So why did Voldemort pick Harry and not Neville? Well, I have a theory for this too. What we don't know about Harry is who is family is, most importantly on his dad's side. What if Harry is the descendant of Godric Griffindor? It would make since that Voldemort, the descendant of Slytherin, would mark Harry
as his equal. This would also make since that Harry would pull the only known relic of GG out of the sorting hat in his second year, AND that his parents lived in
Godric's Hollow.
As for what happened that night I still believe that Harry was made a Horcrux, however unintentionally by LV. Somehow, when LV attempted to kill Harry, something was left inside Harry, some piece of Voldemorts soul. This would explain the connection between the two that time and time again has been presented in the books. This would also count as what Dumbledore had theorized as
something from Griffindor... his heir.
I believe that Harry will die in the seventh book and there are reasons why. A) he will follow in the steps of his mother to
do what is necessary to protect those he loves 
He will finally show the power that the "dark lord knows not" by
making the ultimate act of love... self sacrifice